Optical module producing method and apparatus

ABSTRACT

An optical module is produced by coating, with respect to a substrate having a substrate surface provided with terminal pads and landing pads a solder material on the terminal pads, mounting an optical element package having terminals and a flat top surface on the substrate using the landing pads so that the top surface becomes approximately parallel to the substrate surface and a gap is formed between a bottom surface of the optical element package and the substrate surface, preheating the terminal pads simultaneously as the mounting, and electrically connecting the terminal pads to corresponding terminals of the optical element package by melting the solder material and thereafter hardening the solder material.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to optical module producingmethods and apparatuses, and more particularly to an optical moduleproducing method and an optical module producing apparatus for producingan optical module that mounted with an optical element such as a lightreceiving element.

2. Description of the Related Art

Optical modules are used in various applications, including cameras forvehicles, security systems and the like. The optical module is made upof a substrate, an optical element that is mounted on the substrate. Forexample, the optical element is a CCD or a CMOS device.

There are demands to decrease the size of the optical module withoutdeteriorating the reliability of the optical module. For this reason,the optical element must be accurately positioned relative to thesubstrate, and electrical connections between the optical element andother parts on the substrate must not easily deteriorate with time or inresponse to externally applied shock.

Conventionally, the optical element is mounted on the substratemanually, by manually soldering terminals of the optical element tocorresponding terminals on the substrate.

But when the optical element is mounted on the substrate manually, it isdifficult to accurately position the optical element three-dimensionallyrelative to the substrate surface. If the optical element is not mountedin a parallel state relative to the substrate surface, an optical axisof the optical element will become inclined from a normal to thesubstrate surface, to thereby deteriorate the performance of the opticalmodule.

The optical element may be mounted on the substrate so that the bottomsurface of the optical element makes contiguous contact with thesubstrate surface, to ensure the optical element in a parallel staterelative to the substrate surface. But when the terminals of the opticalelement are soldered to the corresponding terminals on the substrate,the solder easily cracks to deteriorate the reliability of the opticalmodule. The crack in the solder is generated with time when temperaturechanges occur, because the coefficients of thermal expansion are usuallydifferent between the materials used for the substrate and the opticalelement, and the contiguous contact between the optical element and thesubstrate will not allow the stress caused by the difference between thecoefficients of thermal expansion to be absorbed. Moreover, the crack inthe solder is generated in response to an externally applied shock,because the contiguous contact between the optical element and thesubstrate will not allow the shock to be absorbed.

Furthermore, when the terminals of the optical element are manuallysoldered to the corresponding terminals on the substrate, it isdifficult to uniformly control the amount of solder applied to eachterminal, particularly since the intervals of the terminals becomeextremely short as the size of the optical module is reduced.Consequently, it is difficult to uniformly control the reliability ofthe optical modules. In addition, the manual soldering makes itdifficult to manufacture the optical modules with a high efficiency andat a low cost.

For example, a Japanese Laid-Open Patent Application No. 1-4095 proposesa solder supply apparatus that supplies solder paste onto a surfacemount type substrate. A Japanese Laid-Open Patent Application No.9-55565 proposes a printed wiring board that improves the removabilityof the surface mount type parts. A Japanese Laid-Open Patent ApplicationNo. 2006-66418 proposes a mounting apparatus for mounting electronicparts in parallel to a substrate.

Conventionally, there was a problem in that it is difficult to producean optical module having a desired performance and a high reliability,even when the size of the optical module is reduced.

SUMMARY OF THE INVENTION

Accordingly, it is a general object of the present invention to providea novel and useful optical module producing method and apparatus, inwhich the problem described above are suppressed.

Another and more specific object of the present invention is to providean optical module producing method and an optical module producingapparatus, which can produce an optical module having a desiredperformance and a high reliability even when the size of the opticalmodule is reduced.

Still another object of the present invention is to provide an opticalmodule producing method comprising the steps of (a) with respect to asubstrate having a substrate surface provided with terminal pads andlanding pads, coating a solder material on the terminal pads; (b)mounting an optical element package having terminals and a flat topsurface on the substrate using the landing pads so that the top surfacebecomes approximately parallel to the substrate surface and a gap isformed between a bottom surface of the optical element package and thesubstrate surface; (c) preheating the terminal pads simultaneously ascarrying out the step (b); and (d) electrically connecting the terminalpads to corresponding terminals of the optical element package bymelting the solder material and thereafter hardening the soldermaterial. According to the optical module producing method of thepresent invention, it is possible to produce an optical module having adesired performance and a high reliability, even when the size of theoptical module is reduced.

A further object of the present invention is to provide an opticalmodule producing apparatus comprising a movable stage unit on which asubstrate having a substrate surface mounted with terminal pads andlanding pads is set; a coating unit configured to coat a solder materialon the terminal pads when the stage unit moves to a coating position; amounting unit configured to mount an optical element package havingterminals and a flat top surface on the substrate using the landing padswhen the stage unit moves to a mounting position, so that the topsurface becomes approximately parallel to the substrate surface and agap is formed between a bottom surface of the optical element packageand the substrate surface; a preheating part configured to preheat theterminal pads simultaneously as the mounting of the optical elementpackage on the substrate; and a soldering part configured toelectrically connect the terminal pads to corresponding terminals of theoptical element package by melting the solder material and thereafterhardening the solder material. According to the optical module producingapparatus of the present invention, it is possible to produce an opticalmodule having a desired performance and a high reliability, even whenthe size of the optical module is reduced.

Other objects and further features of the present invention will beapparent from the following detailed description when read inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top view showing an optical module;

FIG. 2 is a bottom view showing the optical module;

FIG. 3 is a side view showing the optical module;

FIG. 4 is a top view showing a substrate of the optical module in astate before an optical element package is mounted thereon;

FIG. 5 is a perspective view showing the optical element package;

FIG. 6 is a front view showing an embodiment of an optical moduleproducing apparatus according to the present invention;

FIG. 7 is a side view showing the embodiment of the optical moduleproducing apparatus;

FIG. 8 is a perspective view showing an optical element package supplypart, a heating head part and a bottom heater part;

FIG. 9 is a perspective view showing a positioning head mechanismtogether with a cooling part;

FIGS. 10A and 10B respectively are a front view and a side view showingthe positioning head mechanism;

FIG. 11 is a perspective view showing the positioning head mechanism;

FIG. 12 is a perspective view showing a head cleaning unit;

FIG. 13 is a side view showing the head cleaning unit;

FIG. 14 is a flow chart for explaining an embodiment of an opticalmodule producing method according to the present invention;

FIG. 15 is a diagram showing results of experiments related to surfacematerials of arms of a head heating part conducted by the presentinventors;

FIG. 16 is a diagram showing results of experiments related to effectsof cleaning the arms conducted by the present inventors; and

FIG. 17 is a system block diagram showing a control system of theoptical module producing apparatus.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A description will be given of embodiments of an optical moduleproducing method and an optical module producing apparatus according tothe present invention, by referring to the drawings.

FIG. 1 is a plan view, that is, a top view showing an optical modulethat is produced by the optical module producing method and the opticalmodule producing apparatus according to the present invention, FIG. 2 isa bottom view showing this optical module, and FIG. 3 is a side viewshowing this optical module.

As shown in FIGS. 1 through 3, an optical module 1 has a substrate 11having a top surface (or substrate surface) 11A and a bottom surface11B, and various elements are provided on the top and bottom surfaces11A and 11B. Positioning holes 12, which are used when setting thesubstrate 11 in an optical module producing apparatus and when mountingthe optical module 1 at a desired location on the substrate 11, at thetime of producing the optical module 1, penetrate the substrate 11. Forexample, the substrate 11 is made of FR-4 or FR-5.

The various elements provided on the top surface 11A of the substrate 11include landing pads 13, terminal pads 14 and an optical element package15. The optical element package 15 includes a light receiving elementsuch as a CCD and a CMOS device. The various elements provided on thebottom surface 11B of the substrate 11 include a digital signalprocessor (DSP) package 21 and a connector 22. The DSP package 21processes signals input to and output from the optical element package15. The DSP package 21 is located approximately under the opticalelement package 15 via the substrate 11. The connector 22 is provided toelectrically connect the optical module 1 to an external device (notshown) via a connector (not shown) or a cable (not shown). Otherelements provided on the top and bottom surfaces 11A and 11B of thesubstrate 11 may include inductors, capacitors and resistors.

As will be described later, a gap between the optical element package 15and the substrate surface 11A is determined by the landing pads 13 whenthe optical element package 15 is mounted on the substrate surface 11A.The gap is at least 150 μm so as to enable satisfactory electricalconnection between the terminal pads 14 and terminals 152 of the opticalelement package 15 by solder 31, and may be set in a range of 150 μm to200 μm, for example. An adhesive agent (not shown) may fill the gapbetween the optical element package 15 and the substrate surface 11A.Preferably, the thickness of the landing pads 13 is approximately ⅔ thegap. In the case where the gap is 150 μm, the landing pads 13 preferablyhave a thickness of approximately 100 μm.

FIG. 4 is a plan view, that is, a top view showing the substrate 11 ofthe optical module 1 in a state before the optical element package 15 ismounted thereon, and FIG. 5 is a perspective view showing the opticalelement package 15.

The landing pads 13 may be made of any suitable material and formed onthe substrate surface 11A by a known technique to have a predeterminedthickness with a flat top surface. The terminal pads 14 may be made ofany suitable conductor material, such as Cu, and formed on the substratesurface 11A by a known technique. A predetermined solder pattern, madeof a suitable solder material, is printed on the substrate surface 11Aincluding the terminal pads 14, so as to facilitate the electricalconnection by a solder material during a soldering stage. The landingpads 13 and the terminal pads 14 may be formed simultaneously on thesubstrate surface 11A if the landing pads 13 and the terminal pads 14are made of the same conductor material. In this case, a resist layermay be additionally formed on the conductor layer to form the landingpads 13. The landing pads 13 are exposed and the terminal pads 14 arepartially exposed in a state where the optical element package 15 ismounted on the top surface 11A of the substrate 11, as shown in FIG. 1.

As shown in FIG. 5, the optical element package 15 is made up of aceramic package 150 having recesses 151 in which the terminals 152 areprovided, and a protection layer 153 provided on the ceramic package 150and protecting the light receiving element within the ceramic package150. The protection layer 153 is made of glass having a flat top surfacewhich is approximately perpendicular to an optical axis of the opticalelement package 15. The optical axis of the optical element package 15is approximately normal to the substrate surface 11A in a state wherethe optical element package 15 is mounted on the substrate surface 11A.

The optical element package 15 has a rectangular shape in the plan viewof FIG. 1. For example, the rectangular optical element package 15 has asize of 8.4 mm×8.4 mm in the plan view, and a total of 14 terminals 152are arranged at a pitch of 1 mm. The terminal pads 14 on the substratesurface 11A are arranged at a pitch of 0.6 mm, for example. The landingpads 13 on the substrate surface 11A are provided along confrontingsides of the rectangular optical element package 15 on an outside of therectangular optical element package 15 in the plan view, and each of theterminal pads 14 on the substrate surface 11A and the terminals 152 ofthe optical element package 15 is provided along at least one side ofthe rectangular optical element package 15 with the terminal pads 14extending to an inside of the rectangular optical element package 15 inthe plan view as may be seen by comparing FIG. 1 and FIG. 4. Each of theterminal pads 14 and the terminals 152 is provided along confrontingsides of the rectangular optical element package 15, as shown in FIGS. 4and 5. The landing pads 13 are provided along the confronting sides ofthe rectangular optical element package 15 different from theconfronting sides of the rectangular optical element package 15 alongwhich the terminal pads 14 and the terminals 152 are provided, as shownin FIG. 1.

The terminal pads 14 are electrically connected to correspondingterminals 152 by the solder 31 which includes the printed soldermaterial and the subsequently applied solder material, as shown in FIG.3. For the sake of convenience, FIG. 5 shows the solder 31 thatelectrically connects one pair of terminal pad 14 and terminal 152. Asshown in FIG. 5, the solder 31 extends within the recess 151accommodating the corresponding terminal 152, so as to preventshort-circuiting to an adjacent terminal 152.

The substrate 11 has at least two positioning holes 12 at positionsavoiding the optical element package 15. As shown in FIGS. 1, 2 and 4,two positioning holes 12 are arranged at positions approximately along adiagonal direction of the rectangular optical element package 15 whichis located approximately at the central portion of the substrate surface11A.

The length of each of the terminal pads 14 that is exposed is longerthan a minimum length required to electrically connect the terminal pad14 to the corresponding terminal 152 of the optical element package 15by the solder 31. The length of each of the terminal pads 14 for whichthe printed solder material is provided is less than or equal to theabove minimum length. The length of each of the terminal pads 14 that isexposed may be longer than the minimum length by at least 0.5 mm, andthe upper limit may be appropriately determined based on the availablearea on the substrate surface 11A. A heating portion of the terminal pad14, corresponding to the length of the terminal pad 14 longer than theminimum length, may be used to preheat the terminal pad 14 to a suitabletemperature upon contact with a heating probe when electricallyconnecting the terminal pad 14 and the corresponding terminal 152 of theoptical element package 15 by the solder 31, so as to enable quick andstable melting of the printed solder material and the subsequentlyapplied solder material.

Since the terminal pads 14 are precoated by the printed predeterminedsolder pattern for at least the minimum length thereof, the thermalconduction is promoted by the printed solder material when the soldermaterial is subsequently applied and the solder materials are melted toform the solder 31 that electrically connects the terminal pads 14 tothe corresponding terminals 152 of the optical element package 15. Forthe sake of convenience, it is assumed that the printed solder materialand the subsequently applied solder material are both Sn₃Ag_(0.5)Cu thatenables quick and stable melting of the solder material.

The printed solder material and the subsequently applied solder materialmay be made of the same material but with different compositions.Furthermore, the printed solder material and the subsequently appliedsolder material may be made of mutually different materials. The soldermaterial that is printed may be relatively hard, while it is preferablefor the solder material that is subsequently applied by a dispenser orthe like to be relatively soft and to have an approximately constantviscosity when melted compared to the solder material that is printed.

In this particular case, the substrate 11 and the optical elementpackage 15 (that is, the ceramic package 150) are made of materialshaving mutually different coefficients of thermal expansion, and thesubstrate 11 and the solder 31 are made of materials havingapproximately the same coefficients of thermal expansion. Preferably,the substrate 11 is made of FR-5 having a coefficient of linearexpansion of 17 ppm/C° to 18 ppm/C° in XY directions and 33 ppm/C° in aZ direction, and the solder 31 is made of Sn₃Ag_(0.5)Cu having acoefficient of linear expansion of 21 ppm/C° to 23 ppm/C°. The ceramicpackage 150 has a coefficient of linear expansion of 7 ppm/C° to 8ppm/C° in the XYZ direction. The XY directions are mutuallyperpendicular directions on a plane parallel on the substrate surface11A, and the Z direction is normal to the substrate surface 11A.

Because the landing pads 13 can be formed by a known technique such asthat used during a semiconductor device manufacturing process, it ispossible to control the flatness of the top surface and the thickness ofthe landing pads 13 with a high precision. In addition, the flatness ofthe top surface of the optical element package 15 (that is, the flat topsurface of the protection layer 153) is guaranteed by the manufacturerof the optical element package 15. Therefore, by using the landing pads13 and the top surface of the optical element package 15 to control,with a high precision, the parallel state of the optical element package15 relative to the substrate surface 11A and the gap between the opticalelement package 15 and the substrate surface 11A as will be describedlater, it is possible to make the optical axis of the optical elementpackage 15 approximately normal to the substrate surface 11A in thestate where the optical element package 15 is mounted on the substratesurface 11A, to thereby guarantee a desired performance of the opticalmodule 1. It is also possible to improve the reliability of the opticalmodule 1 by the provision of the gap that is accurately controlled toallow the stress caused by the difference between the coefficients ofthermal expansion of the materials forming the substrate 11 and theoptical element package 15 to be absorbed.

Moreover, when the heating portion of the terminal pad 14, correspondingto the length of the terminal pad 14 longer than the minimum length, isused to preheat the terminal pad 14 to a suitable temperature uponcontact with the heating probe when electrically connecting the terminalpad 14 and the corresponding terminal 152 of the optical element package15 by the printed solder material and the subsequently applied soldermaterial, it is possible to quickly and stably melt the solder materialsand accurately control the amount of solder materials applied to eachconnection, to thereby improve the reliability of the optical module 1.

Furthermore, since the terminal pads 14 are precoated for at least theminimum length thereof by the printed solder material that promotesthermal conduction when the solder 31 electrically connects the terminalpads 14 to the corresponding terminals 152 of the optical elementpackage 15, it is possible to quickly and stably melt the soldermaterials and accurately control the amount of solder materials appliedto each connection, to thereby also improve the reliability of theoptical module 1.

As a result, it is unnecessary to subsequently apply a large amount ofsolder material to ensure positive electrical connection between thecorresponding terminal pad 14 and terminal 152, and consequently preventshort-circuiting of adjacent terminal pads 14 and terminals 152 whichmay otherwise occur if an excessive amount of solder material issubsequently applied. On the other hand, if a small amount of soldermaterial is subsequently applied in order to prevent theshort-circuiting of the adjacent terminal pads 14 and terminals 152, theelectrical connection may be unreliable if the amount of subsequentlyapplied solder material is insufficient, particularly when the gap isprovided between the optical element package 15 and the substratesurface 11A. However, a positive and reliable electrical connection isobtainable in the case described above due to the preheating of theterminal pads 14 and the precoating of the terminal pads 14 made by theprinted solder material.

Of course, the size of the rectangular optical element package 15, thenumber of landing pads 13, and the number of terminals 152 (and theterminal pads 14) are not limited to those described above. The shape ofthe landing pads 13 is also not limited to the approximate rectangularshape shown in FIGS. 1 and 4. In addition, it is possible to provide theterminals 152, and thus the corresponding terminal pads 14, only alongone side of the rectangular optical element package 15. Furthermore, itis not essential to provide the DSP package 21 and the connector 22 onthe bottom surface 11B, that is, on the surface opposite to thesubstrate surface 11A, and at least one of the DSP package 21 and theconnector 22 may be provided on the substrate surface 11A. However, fromthe point of view of efficiently utilizing the limited available area onthe substrate 11, it is preferable to provide the optical elementpackage 15 and the DSP package 21 on opposite surfaces of the substrate11.

Next, a description will be given of an embodiment of the optical moduleproducing apparatus and an embodiment of the optical module producingmethod according to the present invention, by referring to FIGS. 6through 17. It is assumed for the sake of convenience that theembodiments of the optical module producing apparatus and the opticalmodule producing method are used to manufacture the optical module 1described above.

FIG. 6 is a front view showing this embodiment of the optical moduleproducing apparatus according to the present invention, and FIG. 7 is aside view showing this embodiment of the optical module producingapparatus. As shown in FIGS. 6 and 7, an optical module producingapparatus 50 has an X-direction driving shaft 51, a stage unit 52 thatis movable in an X-direction along the X-direction driving shaft 51,first and second Y-direction driving shafts 53, first and secondZ-direction driving shafts 54, a coating unit 55 which is movable alongthe first Y-direction driving shaft 53 in a Y-direction and is movablealong the first Z-direction driving shaft 54 in a Z-direction, amounting unit 56 which is movable along the second Y-direction drivingshaft 53 in the Y-direction and is movable along the second Z-directiondriving shaft 54 in the Z-direction, a temperature control unit 57, aservo controller 58, an operation part 59 including operation buttonssuch as a start button, an optical element package supply part 60, aheating head part 61, a cleaning unit 71, a bottom heater part 81, and acontrol part 91.

The temperature control unit 57 controls the temperature at variousparts of the optical module producing apparatus 50. The servo controller58 controls the movement of the stage unit 51 in the X-direction, andthe movements of the coating unit 55 and the mounting unit 56 in theY-direction. The control part 91 controls the general operation of theentire optical module producing apparatus 50, including the movements ofthe coating unit 55 and the mounting unit 56 in the Z-direction. In thisembodiment, the temperature control unit 57 and the servo controller 58carry out the control under the control of the control part 91.

The substrate 11 shown in FIG. 4 which is precoated by the predeterminedprinted solder pattern (printed solder material) and not yet mountedwith the optical element package 15, is set on the stage unit 52. Withrespect to this substrate 11, the coating unit 55 applies on theterminal pads 14, by a dispenser, a solder material (or solder paste,corresponding to the subsequently applied solder material describedabove) which will be melted together with the printed solder materialduring a subsequent soldering stage that uses the heating head part 61to melt the solder materials and electrically connect the terminal pads14 to the corresponding terminals 152 of the optical element package 15by the solder 31. The solder material is applied to the terminal pads 14that have also been precoated by the printed solder material, by movingthe coating unit 55 in the Y-direction under the control of the servocontroller 58 and in the Z-direction under the control of the controlpart 91, and moving the stage unit 52 in the X-direction under thecontrol of the servo controller 58.

Next, the stage unit 52 is moved in the X-direction to the position ofthe heating head part 61 under the control of the servo controller 58.The mounting unit 56 is moved in the Y-direction under the control ofthe servo controller 58 and in the Z-direction under the control of thecontrol part 91 to catch the optical element package 15 that is suppliedby the optical element package supply part 60 by a suction head 101, andplaces the optical element package 15 on the substrate 11 that is set onthe stage unit 52.

FIG. 8 is a perspective view showing the optical element package supplypart 60, the heating head part 61 and the bottom heater part 81.Further, FIG. 9 is a perspective view showing a positioning headmechanism together with a cooling part. FIGS. 10A and 10B respectivelyare a front view and a side view showing the positioning head mechanism,and FIG. 11 is a perspective view showing the positioning headmechanism.

The heating of the substrate 11 from the bottom surface 11B by thebottom heater part 81, and the positioning of the optical elementpackage 15 with respect to the substrate 11 by the positioning headmechanism of the mounting unit 56, are carried out simultaneously. Thebottom heater part 81 heats the bottom surface 11B by blowing hot airvia holes in the stage unit 52 for a predetermined time so as to preparefor quick and stable melting of the solder material, under the controlof the temperature control unit 57. In addition, the heating probes (notshown) of the heating head part 61 contact the heating portions of theterminal pads 14 under the control of the control part 91, and preheatthe terminal pads 14 to a suitable temperature under the control of thetemperature control unit 57. On the other hand, the positioning headmechanism lowers legs 102 of the suction head 101 in the Z-directiononto the corresponding landing pads 13 on the substrate surface 11A,under the control of the control part 91, to thereby position theoptical element package 15 in a parallel state relative to the substratesurface 11A with the gap between the optical element package 15 and thesubstrate surface 11A accurately controlled to the desired value. Thepositioning head mechanism forms a copying mechanism for making the topsurface of the optical element package 15 copy the substrate surface11A. Only one of the bottom heater part 81 and the heating probes may beprovided. In addition, the bottom heater part 81 and/or the heatingprobes form a preheating means.

Thereafter, a pair of arms of the heating head part 61 is lowered in theZ-direction to make contact with the solder materials that will form thesolder 31 when hardened, under the control of the control part 91, andmelts the solder materials to electrically connect the terminal pads 14to the corresponding terminals 152 of the optical element package 15when the pair arms is heated to a desired temperature under the controlof the temperature control part 57. A temperature sensor (not shown) isprovided in a vicinity of the pair of arms, and the temperature controlpart 57 detects the temperature of the arms based on a detection signaloutput from this temperature sensor. After raising the arms of theheating head part 61 in the Z-direction away from the substrate 11,under the control of the control part 91, a cooling part 103 shown inFIG. 9 blows air over the solder material so as to harden the meltedsolder material to form the solder 31, under the control of thetemperature control part 57. The heating head part 61 and the coolingpart 103 form a soldering means.

Preferably, the arms of the heating head part 61 have a cross sectionalshape that permits heat to efficiently conduct to the solder material.In this particular case, each arm has a cross sectional shape such thatthe cross sectional area along a plane parallel to the XZ plane in FIG.8 gradually decreases towards the portion of the arm that makes contactwith the solder material.

FIG. 12 is a perspective view showing the head cleaning unit 71, andFIG. 13 is a side view showing the head cleaning unit 71. The headcleaning unit 71 cleans the heating head part 61 at an arbitrary timing,under the control of the control part 91, to remove residual flux on theheating head part 61 and improve the heating or melting stability of thesolder 31. More particularly, the head cleaning unit 71 has a pluralityof blades that move in the Y-direction against the lower surface of thepair of arms of the heating head part 61 as indicated by FL in FIG. 13,so as to scrape off the residual flux adhered on the lower surface ofthe pair of arms.

FIG. 14 is a flow chart for explaining this embodiment of the opticalmodule producing method according to the present invention.

In FIG. 14, the substrate 11 is set on the stage unit 52 in a step S1,manually by an operator or, automatically by a robot (not shown), andthe control part 91 detects that the substrate 11 is set on the stageunit 52 in response to a detection signal output from a substrate sensor(not shown) of the stage unit 52. The optical module producing processis started in a step S2 when the operator pushes the start button on theoperation part 59, by the control part 91 which detects a start signalthat is issued by the pushing of the start button. The stage unit 52 ismoved in the X-direction to a working position (that is, a coatingposition) of the coating unit 55 in a step S3, under the control of theservo controller 58. The coating unit 55 applies on the terminal pads14, by the dispenser in a step S4, under the control of the control part91, the solder material (or solder paste, corresponding to thesubsequently applied solder material described above) which will bemelted together with the printed solder material during the subsequentsoldering stage that uses the heating head part 61 to melt the soldermaterials and electrically connect the terminal pads 14 to thecorresponding terminals 152 of the optical element package 15 by thesolder 31.

The step S4 includes steps S41 through S47. The coating unit 55 islowered in the Z-direction in the step S41, and the solder material isdispensed on the terminal pad 14 in the step S42. The stage unit 52 ismoved in the X-direction so as to apply and coat the solder material onthe terminal pad 14 for at least the minimum length described above inthe step S43, and the dispensing of the solder material is stopped inthe step S44. The coating unit 55 is raised in the Z-direction in thestep S45, and a step S46 decides whether or not all of the terminal pads14 on the substrate 11 have been coated by the solder material. Theprocess advances to a step S5 if the decision result in the step S46 isYES. On the other hand, if the decision result in the step S46 is NO,the stage unit 52 is moved in the X-direction and/or the coating unit 55is moved in the Y-direction in the step S47 so as to prepare for thecoating of the next terminal pad 14, and the process returns to the stepS41.

The stage unit 52 is moved in the X-direction to a working position(that is, a mounting position) of the mounting unit 56 in the step S5,under the control of the servo controller 58. The optical elementpackage 15 is set on the optical element package supply part 60 in astep S6, manually by the operator or, automatically by a robot (notshown). A step S7 decides whether or not the optical element package 15is set on the optical element package supply part 60 in response to anoutput of a supply part sensor (not shown) which detects the opticalelement package 15. The control part 91 can detect if the opticalelement package 15 is set on the optical element package supply part 60in response to the output of the supply part sensor. If the decisionresult in the step S7 becomes YES, the mounting unit 56 is moved in theY-direction above the optical element package supply part 60 in a stepS8, under the control of the servo controller 58, and is lowered in theZ-direction in a step S9 under the control of the control part 91. Themounting unit 56 catches the optical element package 15 that is set onthe optical element package supply part 60 by the suction head 101 in astep S10, under the control of the control part 91, and a step S11decides whether or not the optical element package 15 has been caught bythe suction head 101 in response to an output of a suction head sensor(not shown) which detects the optical element package 15. The controlpart 91 can detect if the suction head 101 has caught the opticalelement package 15 in response to the output of the suction head sensor.If the decision result in the step S11 becomes YES, the mounting unit 56is raised in the Z-direction in a step S12, under the control of thecontrol part 91. The mounting unit 56 is then moved in the Y-directionabove the substrate 11 on the stage unit 52 in a step S13, under thecontrol of the servo controller 58.

Steps S14 through S20 and steps S21 through S23 are carried outsimultaneously. The bottom heater part 81 is raised in the Z-directionunder the control of the control part 91, and the heating probes of theheating head part 61 contact the heating portions of the terminal pads14 under the control of the control part 91 and preheat the terminalpads 14 to a suitable temperature under the control of the temperaturecontrol unit 57, in the step S21. The bottom heater part 81 blows hotair via the holes in the stage unit 52 onto the bottom surface 11B ofthe substrate 11 for a predetermined time of 10 seconds, for example, inthe step S22, under the control of the temperature control unit 57, soas to prepare for quick and stable melting of the solder materials onthe terminal pads 14. The bottom heater part 81 stops blowing the hotair under the control of the temperature control unit 57 and is loweredin the Z-direction under the control of the control part 91 after thepredetermined time in the step S23. In addition, the heating probes ofthe heating head part 61 separate from the terminal pads 14 under thecontrol of the control part 91.

On the other hand, the mounting unit 56 carrying the optical elementpackage 15 is lowered in the Z-direction in the step S14, under thecontrol of the control part 91. The positioning head mechanism of themounting unit 56 lowers the legs 102 of the suction head 101 onto thecorresponding landing pads 13 on the substrate surface 11A, and pushesdown on the landing pads 13 for a predetermined time of 10 seconds, forexample, in the step S15, under the control of the control part 91, tothereby position the optical element package 15 in a parallel staterelative to the substrate surface 11A with the gap between the opticalelement package 15 and the substrate surface 11A accurately controlledto the desired value. The arms of the heating head part 61 are loweredin the Z-direction to a position to make contact with the soldermaterial under the control of the control part 91, and the pair of armsof the heating head part 61 is heated to a desired temperature under thecontrol of the temperature control part 57, in the step S16, so as tomelt the solder material in contact with each arm. Preferably, thetemperature of each arm is raised to the desired temperature by beforeeach arm makes contact with the solder material. Accordingly, theoptical element package 15 is positioned to the state parallel withrespect to the substrate surface 11A, with the gap between the opticalelement package 15 and the substrate surface 11A accurately controlledto the desired value, and the solder material for electricallyconnecting the terminal pads 14 and the corresponding terminals 152 ofthe optical element package 15 is melted. The pair of arms of theheating head part 61 is raised in the Z-direction under the control ofthe control part 91, in the step S17. The cooling part 103 blows airover the solder material for a predetermined time of 4 seconds, forexample, in the step S18, under the control of the control part 91 orthe temperature control unit 57, so as to harden the melted soldermaterials to form the solder 31. Thereafter, the mounting unit 56 israised in the Z-direction in the step S19, under the control of thecontrol part 91, and the stage unit 52 is moved in the X-direction inthe step S20, under the control of the servo controller 58, to an unloadposition where the completed optical module 1 may be removed from thestage unit 52 manually by the operator or, automatically by a robot (notshown).

According to experiments conducted by the present inventors, it wasconfirmed that, for the optical module 1 mounted with the opticalelement package 15 having the size described above and the number ofterminal pads 14 described above, the optical element package 15 can beguaranteed to be approximately parallel to the substrate surface 11A,and that the mounting error is only within a range of ±50 μm from theperfectly parallel state and is effectively suppressed.

At least the surface portion of the pair of arms of the heating headpart 61 that makes contact with the solder material may be made of SUS,Cu+Cr, G04+Cr and the like. FIG. 15 is a diagram showing results ofexperiments related to surface materials of the arms of the head heatingpart 61 conducted by the present inventors. According to experimentsconducted by the present inventors, it was confirmed that Cu+Cr orG04+Cr is preferable as the arm surface material from the point of viewof the relatively short time it takes for the arm temperature to rise toa desired temperature of approximately 300° C. or higher, as indicatedby symbols “o” in FIG. 15. But from the point of view of the durabilityof the arm even when the surface is scraped by the blades of the headcleaning unit 71, it was confirmed that SUS or G04+Cr is preferable asthe arm surface material, as indicated by symbols “o” in FIG. 15. InFIG. 15, symbols “x” indicate that the material is not suited for thearm surface material from the point of view of the melting start time ordurability. Therefore, it was confirmed that G04+Cr is particularlypreferable for use as the arm material forming at least the surfaceportion of the pair of arms of the heating head part 61.

FIG. 16 is a diagram showing results of experiments related to effectsof cleaning the arms conducted by the present inventors. According toexperiments conducted by the present inventors, it was also found thatthe flux that adheres on the surface of the pair of arms of the heatinghead part 61 after repeated heating and melting of the solder materialsgradually increases the solder melting time. It was found that thesolder material melting time increases from approximately 1 second toapproximately 10 seconds as shown in FIG. 16 after the heating head part61 carries out the solder melting operation with respect to 50 opticalmodules 1 mounted with the optical element package 15 having the sizedescribed above and the number of terminal pads 14 described above.Hence, it was found that the solder material melting time is effectivelyreduced by manually cleaning the arms of the heating head part 61 forevery 50 optical modules 1, for example, as shown in FIG. 16.Furthermore, it was also found that the solder material melting time iseffectively reduced to approximately 5 seconds or less, for example, asindicated by a bold arrow in FIG. 16, by automatically carrying out thecleaning periodically as indicated by dotted lines in FIG. 16.

FIG. 17 is a system block diagram showing a control system of theoptical module producing apparatus 51. The control system shown in FIG.17 includes the servo controller 58, the temperature control part 57 andthe control part 91. The detection signals output from the varioussensors described above are input to the control part 91. The controlpart 91 controls a Z-direction driving part 603 which drives and movesthe coating unit 55, the mounting unit 56 and the heating head part 61in the Z-direction. The control part 91 also carries out various controloperations with respect to various parts of the optical module producingapparatus 51. Of course, the Z-direction driving part 603 may be formedby a plurality of driving means for driving the coating unit 55, themounting unit 56 and the heating head part 61.

The servo controller 58 controls an X-direction driving part 601 fordriving and moving the stage unit 52 in the X-direction, under thecontrol of the control part 91. In addition, the servo controller 58controls a Y-direction driving part 602 for driving and moving thecoating unit 55 and the mounting unit 56 in the Y-direction, under thecontrol of the control part 91. The temperature control part 57 controlsthe bottom heater part 81, the cooling part 103, the heating probes ofthe heating head part 61 and the like, under the control of the controlpart 91. Of course, the Y-direction driving part 602 may be formed by aplurality of driving means for driving the coating unit 55 and themounting unit 56.

This application claims the benefit of a Japanese Patent Application No.2006-291992 filed Oct. 27, 2006, in the Japanese Patent Office, thedisclosure of which is hereby incorporated by reference.

Further, the present invention is not limited to these embodiments, butvarious variations and modifications may be made without departing fromthe scope of the present invention.

1. An optical module producing method comprising the steps of: (a) withrespect to a substrate having a substrate surface provided with terminalpads and landing pads, coating a solder material on the terminal pads;(b) mounting an optical element package having terminals and a flat topsurface on the substrate using the landing pads so that the top surfacebecomes approximately parallel to the substrate surface and a gap isformed between a bottom surface of the optical element package and thesubstrate surface; (c) preheating the terminal pads simultaneously ascarrying out the step (b); and (d) electrically connecting the terminalpads to corresponding terminals of the optical element package bymelting the solder material and thereafter hardening the soldermaterial.
 2. The optical module producing method as claimed in claim 1,wherein the step (b) determines the gap by pushing legs of a positioninghead mechanism against the landing pads in a state where the top surfaceof the optical element package is held by the positioning headmechanism, and the step (d) causes heated arms of a heating head part tomake contact and melt the solder material in the state where the gap isdetermined.
 3. The optical module producing method as claimed in claim1, wherein the step (c) preheats the substrate from a side opposite tothe substrate surface.
 4. The optical module producing method as claimedin claim 1, wherein the step (c) preheats the terminal pads by causingheating probes to make contact with portions of the terminal pads notcoated with the solder material.
 5. The optical module producing methodas claimed in claim 1, wherein the terminal pads are precoated with asolder material prior to the step (a).
 6. The optical module producingmethod as claimed in claim 1, wherein the gap is at least 150 μm.
 7. Theoptical module producing method as claimed in claim 1, wherein theoptical element package comprises a CCD or a CMOS device, and the step(b) mounts the optical element package on the substrate surface so thatan optical axis of the optical element package is approximately normalto the substrate surface.
 8. The optical module producing method asclaimed in claim 1, wherein the optical element package has arectangular shape in a plan view, the landing pads are provided on thesubstrate surface along confronting sides of the rectangular opticalelement package in the plan view, and the terminal pads are provided onthe substrate surface along corresponding sides of the rectangularoptical element package in the plan view.
 9. The optical moduleproducing method as claimed in claim 8, further comprising the steps of:(e) setting the substrate on a stage unit using a pair of positioningholes that penetrate the substrate, and the positioning holes arearranged at positions avoiding the rectangular optical element packageand approximately along a diagonal direction of the rectangular opticalelement package.
 10. An optical module producing apparatus comprising: amovable stage unit on which a substrate having a substrate surfacemounted with terminal pads and landing pads is set; a coating unitconfigured to coat a solder material on the terminal pads when the stageunit moves to a coating position; a mounting unit configured to mount anoptical element package having terminals and a flat top surface on thesubstrate using the landing pads when the stage unit moves to a mountingposition, so that the top surface becomes approximately parallel to thesubstrate surface and a gap is formed between a bottom surface of theoptical element package and the substrate surface; a preheating partconfigured to preheat the terminal pads simultaneously as the mountingof the optical element package on the substrate; and a soldering partconfigured to electrically connect the terminal pads to correspondingterminals of the optical element package by melting the solder materialand thereafter hardening the solder material.
 11. The optical moduleproducing apparatus as claimed in claim 10, wherein: the mounting unithas a positioning head mechanism that has legs, and determines the gapby pushing the legs of the positioning head mechanism against thelanding pads in a state where the top surface of the optical elementpackage is held by the positioning head mechanism; and the solderingpart has arms, and causes heated arms to make contact and melt thesolder material in the state where the gap is determined.
 12. Theoptical module producing apparatus as claimed in claim 10, wherein thepreheating part has a bottom heater part configured to preheat thesubstrate from a side opposite to the substrate surface.
 13. The opticalmodule producing apparatus as claimed in claim 10, wherein thepreheating part has heating probes configured to preheat the terminalpads by making contact with portions of the terminal pads not coatedwith the solder material.
 14. The optical module producing apparatus asclaimed in claim 10, wherein the terminal pads of the substrate that isset on the stage unit that has moved to the coating position areprecoated with a solder material.
 15. The optical module producingapparatus as claimed in claim 10, wherein the gap is at least 150 μm.16. The optical module producing apparatus as claimed in claim 10,wherein the optical element package comprises a CCD or a CMOS device,and the mounting unit mounts the optical element package on thesubstrate surface so that an optical axis of the optical element packageis approximately normal to the substrate surface.
 17. The optical moduleproducing apparatus as claimed in claim 10, wherein the optical elementpackage has a rectangular shape in a plan view, the landing pads areprovided on the substrate surface along confronting sides of therectangular optical element package in the plan view, and the terminalpads are provided on the substrate surface along corresponding sides ofthe rectangular optical element package in the plan view.
 18. Theoptical module producing apparatus as claimed in claim 17, wherein thesubstrate is set on the stage unit using a pair of positioning holesthat penetrate the substrate, and the positioning holes are arranged atpositions avoiding the rectangular optical element package andapproximately along a diagonal direction of the rectangular opticalelement package.